JPS6360479B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for mounting a magnetic bubble memory chip on a substrate while reducing distortion.

Magnetic bubble memory chips are made of non-magnetic garnet crystal wafers with a thickness of approximately 500 μm, such as gadolinium.
Magnetic garnet with the required magnetic properties is epitaxially grown on a wafer made of single crystal gallium garnet (Gd ₃ Ga ₅ O ₁₂ ) to a thickness of several μm, and then thin film deposition technology and photo-etching technology are applied on this wafer. It consists of a conductor pattern layer and a drive pattern layer that are insulated and formed using (photolithography) and then cut into memory chips, with circuits formed on a microcrystalline film.

For example, in the case of a memory chip with a storage capacity of 64K bits that uses magnetic bubbles with a diameter of 3 μm as the memory medium, the size of the chip is approximately 6 mm x 5 mm, and in the case of a 1M bit memory that uses magnetic bubbles with a diameter of 1.9 μm, the chip size is The size is approximately 10 mm x 10 mm, and the thickness of the chip is determined by the thickness of the substrate crystal, so each chip may be formed from an extremely thin magnetic crystal film.

Such a memory chip is bonded onto a printed wiring board (hereinafter referred to as the board for short), wiring connections are made, and then packaging as a magnetic bubble memory is performed.

FIG. 1 shows a board on which such a memory chip is mounted, and A is a front view thereof, and B is a sectional view taken along the line A-A'.

In Fig. 1, the memory chip is mounted in the central recess 2 of the board 1 with adhesive, and then the wiring terminal part of the memory chip and the wiring terminal part on the board are connected to each other by wire bonding, and the wiring is connected to the board terminal 3 by the wiring inside the board. When packaging the cable, it is welded and connected to the embedded terminals of the resin package, which has a dual in-line structure. Note that the deep notch 4 provided in the substrate 1
is a notch for inserting a drive coil for forming a drive magnetic field for transferring magnetic bubbles.

Now, conventionally, memory chips are mounted on the substrate 1 using an adhesive as described above.
When using a heat-curing adhesive, the heat curing speed varies depending on the location within the memory chip, and the curing does not occur uniformly, resulting in distortion.On the other hand, when using a room-temperature-curing adhesive, it takes time to cure, and in this case, In both cases, the shrinkage of the resin causes distortion in the memory chip, deteriorating the magnetic properties of the memory chip.

FIG. 2 shows a state in which the memory chip 5 is bent due to the distortion that occurs when the memory chip 5 is attached to the central recess 2 of the substrate 1 shown in FIG. 1 using an adhesive 6. That is, in both heat curing and room temperature curing, distortion occurs because the curing occurs from the periphery of the adhesive 6 that is in contact with the memory chip 5, but since the memory chip 5 is thin, curvature occurs, and this curvature The mechanical distortion caused by this directly affects the magnetic properties of the memory chip 5, and appears as a reduction in the operating magnetic field area in the magnetic bubble memory, particularly in the collapse magnetic field area.

Conventionally, alumina porcelain has often been used as the substrate 1 on which memory chips are mounted, but recently substrates made of glass epoxy or polyimide resin have come into widespread use due to their characteristics such as workability and heat resistance. .

Here, the coefficient of thermal expansion of the magnetic bubble memory chip is
9.5×10 ^-6 deg ^-1 , whereas the thermal expansion coefficient of the above resin is relatively small at 3 to 7×10 ^-1 deg ^-1 in the operating temperature range, but it has the property of increasing rapidly at high temperatures. .

FIG. 3 shows the temperature dependence of the thermal expansion coefficient of the heat-resistant resin, which is characterized by a rapid increase above 160°C.

The purpose of the present invention is to avoid the deterioration of magnetic properties caused by distortion caused by adhesion when mounting a memory chip on a substrate, and for this purpose, heat-resistant resin such as glass epoxy or polyimide is used. Taking advantage of the property that the coefficient of thermal expansion of the substrate increases rapidly at high temperatures, the memory chip is inserted into the recess of the substrate after the substrate is heated to a high temperature and expanded sufficiently, and then the temperature is lowered to room temperature. The gist of this is to mount a memory chip on a board without any problems.

Figure 4 shows an embodiment of the present invention.
There is a recess 2 of ×10 mm square, and the chip size is determined in this.
This is the cross-sectional shape when a 10 x 10 mm square memory chip 5 is mounted, and in this case, the size of the substrate recess 2 must be set to a value approximately equal to the room temperature size of the memory chip 5 at the memory chip insertion temperature, for example, 200°C. be.

As for the mounting method, if the board 1 is heated to about 200°C, the board 1 will expand, while the memory chip 5 will be at room temperature, so if it is inserted in this state and then cooled to room temperature, the memory chip 5 will be sandwiched between the board 1. The mounting is completed after it is fixed in place.

FIG. 5 shows a structure in which the reliability of the clamping and fixing shown in FIG. 4 is improved, and by providing a protrusion 7 around the recess 2 of the substrate 1, the clamping and fixing of the memory chip is ensured.

Now, when sandwiching a magnetic material such as a magnetic memory chip, magnetostriction may occur due to pressure from the surroundings, which may deteriorate the magnetic properties of the memory chip, but resins such as glass epoxy or polyimide are Unlike a rigid body, it has slight elasticity and the clamping force is relatively weak, so when it was mounted using the method of the present invention, no deterioration in magnetic properties could be observed.

In the present invention, various attempts have been made to reduce the occurrence of distortion when mounting a memory chip on a substrate, but all of them used adhesives, and it was not possible to avoid the effects of condensation distortion to some extent. In contrast, mounting is performed without using adhesive, and by implementing the present invention, it has been possible to avoid deterioration of magnetic properties when mounting memory chips.

[Brief explanation of the drawing]

Figure 1 shows a printed wiring board on which a magnetic memory chip is mounted, A is a front view, B is a sectional view taken along the line A-A',
Figure 2 is a cross-sectional view showing how conventional adhesive strain occurs.
FIG. 3 shows the thermal expansion characteristics of the resin substrate, and FIGS. 4 and 5 are cross-sectional views of a device mounted on which the present invention is implemented. In the figure, 1...printed wiring board, 2...substrate recess on which a memory chip is mounted, 5...memory chip, 6...adhesive, 7...protrusion.

Claims (1)

[Claims] 1. A material such as glass epoxy or polyimide, which has a small coefficient of thermal expansion at least in the operating temperature range of the magnetic bubble memory chip, and whose thermal expansion coefficient rapidly increases at high temperatures above the operating temperature range. A magnetic bubble memory board made of heat-resistant resin is provided, the board has a recess for accommodating and fixing the magnetic bubble memory chip, and the magnetic bubble memory chip is heated to the high temperature while the board is heated to the high temperature. By fitting into the recess and then cooling the substrate, the inner circumferential surface of the recess of the substrate clamps the outer circumferential surface of the magnetic bubble memory chip without an adhesive, thereby fixing the magnetic bubble memory chip. A method for mounting a magnetic bubble memory chip featuring: